This invention relates to a photometer with interchangeable calibration cards, more particularly one consisting essentially of a galvanometer and a zone containing an orifice for a cell.
In colorimetry, one of the analytical procedures very commonly used in chemical analysis, the substances to be measured in solution are converted, by the addition of a reagent, into color compounds. From the resultant color intensity, concentration of the substance in the solution can be derived. Instruments used to measure color intensity are photoelectric colorimeters or spectrophotometers. In certain fields of analysis, photometers with interchangeable scales calibrated direct in concentrations are used. Each calibration scale is suited to a specific method of measurement, for which there is frequently a ready-for-use reagent kit. In each case, however, a number of parameters must be fixed before carrying out a measurement on the photometer. In the case of a colorimeter of simple construction, these parameters are, for example, the choice of the appropriate wavelength, the choice of the size of cell and the setting of the apparatus to the so-called zero extinction., viz., setting to the blank value. In actual practice, one of these parameters is frequently set incorrectly. For example, the wavelength from the preceding determination may not be changed or incorrect instructions, which are not suited to the calibration scale, are erroneously selected.